1. Field of the Invention
The present invention relates to a method for generating an NC (numerical control) program which is used when an NC machine equipped with an end mill serving as a cutting tool cuts into a relatively simple shape, and which determines the tool path of the end mill together with the feed rate in each portion of the tool path such as to decrease wear and damage to the cutting tool and thereby permit as efficient and accurate cutting as possible. The present invention also relates to a computer program and a recording medium storing it.
2. Description of the Related Art
In NC machines for moving a cutting tool along a tool path defined in advance numerically relative to a workpiece fixed on a machining table and thereby machining the workpiece in a predetermined manner, in order to meet the requirements for improvements in machining efficiency and accuracy and for extended life of the cutting tool, it is important to determine appropriately the tool path of the cutting tool together with the feed rate in each portion of the tool path.
In order to meet such requirements, the present inventors has proposed a method for generating tool paths having an appropriate feed rate pattern for drilling and tapping (Japanese Patent Application Laid-Open No. 11-156672 (1999)). This method has been devised with considering the fact that the majority of drilling and tapping are carried out by repeating a canned cycle of the operations of positioning a cutting tool at a machining position; protruding the cutting tool; cutting the workpiece; reaching the target depth; reversing the cutting tool; and retracting the cutting tool. More specifically, in the method, various tool paths for the cutting tool together with the feed rate pattern for each process are determined in advance depending on various machining conditions such as cutting-tool sizes, workpiece material types, and machining depths, and thereby stored in a database, whereby in each process, path data corresponding to a specified machining condition is automatically selected, and then the cutting tool is operated by a servo system on the basis of the selected path data. As such, desired machining is carried out.
According to this method, drilling and tapping are carried out with appropriate cutting-tool feed rates throughout the tool path during the machining and the intermission thereof. Accordingly, the machine tool achieves maximum performance, that is, high machining efficiency and high machining accuracy. Further, the data stored in the database used for the selection of the tool path is renewed on the basis of the detection result of the internal state of the servo system during the machining. This avoids obsolescence of the machine tool, and thereby maintains the high machining efficiency and the high machining accuracy.
NC machines are used not only in a state equipped with a drill or a tap as described above, but also widely in a state equipped with an end mill for cutting the workpiece surface into a diverse shape. In such a case, an operator prepares an NC program for indicating the tool path of the cutting tool, whereby the feeding of the end mill is controlled according to the NC program.
Nevertheless, such an NC program is prepared for each specific desired machining shape on the basis of the operator's skill. As a result, even for an identical machining shape, various NC programs are prepared which have different control parameters such as: the positions of the start and end points of the tool path; and the feed rate and the cutting pitch between the start and end points. As such, it is difficult for unskilled operators to achieve satisfactory machining efficiency and accuracy. Further, in case that an inappropriate NC program is prepared, this program can cause various problems such as: damage or chipping to the cutting tool; and shortened life of the cutting tool due to excessive wear.
Further, even when an NC program is carefully prepared by a skilled operator, the program does not necessarily have the best performance. Thus, there has been the possibility of losing an opportunity of improving the machining performance.